A muffler is conventionally connected to the outlet from an internal combustion engine to reduce the noise of the exhaust gas stream. The muffler characteristically includes an expansion chamber between its inlet and outlet, which itself will reduce the sound level. In addition, the muffler is often provided with a packing such as glass fibers, or channel means that divide the stream to produce interferences effects which themselves may reduce the sound level.
It is a feature of internal combustion engines, both two cycle and four cycle, that their efficiency is in part a function of the characteristics of its exhaust system. The engine's performance will be improved if the characteristics of the muffler, such as back pressure, match the engine's requirements over a wide range of operating conditions from idling to increased performance. The problem is that the conventional muffler is a fixed and static device that is not operationally adjustable. For this reason its design is a compromise to give better service at a selected performance level, and lesser service at other performance levels. Thus, a muffler which is a very suitable for racing operations may be only marginally acceptable for regular street operation, and one which is suitable for street operations may be only marginally acceptable for high speed operation, and perhaps is also marginally acceptable in all cases at idle. In fact, in high performance operation a conventional muffler may be a poor companion if it must preferably function best at idle.
A muffler to attend to the varying performance requirements should be adjustable to provide an adjustable response, but none is known to exist. This invention provides adjustable means which can be automatically or manually adjusted during operation to respond to the engine performance requirements. In its preferred embodiments, the adjustment will be automatic because a motorcycle rider or the driver of a high performance vehicle, for example, has enough to do already without adjusting the muffler. Automatic adjustments can include means responsive to the exhaust gas stream, and also linkages responsive to throttle settings and other engine parameters. Manual adjustment is also possible although less desirable, such as by means of hand actuated cables and levers that are available to the operator during operation.
This invention comprehends usage in all types of mobile and fixed engine installations, for example, stationary and portable power plants, automobiles, trucks, and motorcycles.
The inventor herein has found that a conventional muffler can be made to be responsive to engine performance in such a way as to improve the engine's efficiency and output by providing an adjustable variable restrictor at the exhaust end of the muffler, and that depending on the engine a throttling down or an opening up at this point with increased exhaust stream flow, does in fact appreciably increase the engine output compared to the same installation and engine setting utilizing the same muffler but without the variable restrictor, while still providing good performance at idle.
It is an object of this invention is to accomplish this objective with a muffler which is automatically responsive to the performance of the engine, and also or instead manually if preferred.